Ultraviolet (UV) and fluorescent lamps are used in a wide range of applications. For example, such lamps are used in medical, horticultural, and Heating, Ventilation and Air Conditioning (HVAC) settings, as well as the common and prolific use of fluorescent lamps as sources of visible light. In any of these and other diverse settings, the lamps may be subject to high ambient temperatures depending on their particular use. For instance, lamps may be used in garages, attics, or other specialized locations where ambient temperatures can reach very high levels.
Ballasts are used with UV and fluorescent lamps as a means for starting lamp operation by providing the requisite voltage to establish the arc that initially causes the lamp to turn on. More particularly, the ballast strikes an arc within a UV/fluorescent lamp at start-up by placing a high potential across the lamp's filaments. Ballasts often come equipped with mechanical thermal protection to shut down in high temperature conditions. For example, the internal thermal protection mechanism in a ballast may shut down ballast operation, thereby opening the circuit, where the ballast temperature reaches a certain cutout temperature of the protection mechanism. The ballast temperature will generally decrease when it is no longer conducting current, and the thermal protection mechanism will therefore allow the ballast to resume current conduction which allows the lamps to be powered on again. The ambient temperature may still be high however, causing the ballast temperature to quickly reach the cutout temperature and again shut down ballast operation. This thermal cycle can continue indefinitely, until the ambient temperature decreases sufficiently to break the cycle.
During this time, both the ballast and the lamps will repeatedly cycle between on and off, while providing less than useful lamp operating time. Moreover, this thermal cycling adversely affects the longevity of the lamp, as these types of products age the most during their start-up cycles. This is largely due to the physics underlying UV/fluorescent lamp operation. More specifically, UV and fluorescent lamps generally include a sealed glass tube that includes a small amount of mercury and an inert gas. The tube generally includes two electrodes or “filaments,” one at each end of the tube, which are wired to an electrical circuit coupled to an alternating current (AC) power source. When the lamp is initially turned on, electricity heats up the filaments, which boils off electrons from the metal surface into the gas tube, which in turn ionizes the gas and creates an electrically conductive medium. At this point, the lamp's ballast provides the voltage kick across the filaments to establish an electrical arc through the gas. The resulting collision of free electrons with atoms releases other electrons, which creates ions, and ultimately plasma which establishes a path for an electrical current. Each time a lamp is turned on, the filament boils off electrons from its metal surface to ionize the gas and establish the arc, whereby a small amount of filament material actually evaporates. The number of start-ups that a lamp can undergo is thus limited before the filament ultimately burns out. Today's UV and fluorescent products are currently estimated to withstand approximately 4500 starts before failure. The thermal cycles caused by high ambient temperatures and the ballast's internal thermal protection mechanism cause an excessive number of lamp starts, which degenerates the integrity of the filament, ultimately leading to premature lamp mortality.
Accordingly, there is a need for a system and method for increasing lamp life that otherwise could be degraded due to thermal cycling resulting from high ambient temperatures and the internal thermal protection mechanisms provided by ballasts. The present invention fulfills these and other needs, and offers other advantages over the prior art.